1. Field of the Invention
The invention relates to glass fibers and somewhat more particularly to a method of increasing the breaking strength of glass fibers such as generally utilized in optical communication techniques.
2. Prior Art
An essential property characteristic of glass fibers, particularly optical glass fibers, is the breaking strength thereof. The largest possible minimum breaking strength of glass fibers is required, not only for further processing of raw fibers into finished optical cables and the like, but also in the actual utility of light-conductive fibers and/or cables. Even during continuous operational behavior, the breaking strength of glass fibers should not fall below a minimum level.
The breaking behavior of glass fibers is characterized by a lack of a flow range and a specific dependency of breakage statistics on a sample length thereof, both of which indicate the effect of localized flaws on the surface and in the volume or cross-section of a glass fiber [see D. Kalish et al., "Probability of Static Fatigue Failure in Optical Fibers," Applied Physics Letters, Vol. 28, (1976) pp. 721-723 and/or E. Helfand et al., "Statistics of the Strength of Optical Fibers," J. Applied Physics, Vol. 48, (1977) pp. 3251-3259]. Such local flaws may be geometric irregularities, such as micro-fissures, dust inclusions, bubbles, etc., [see R. D. Mauer, "Effect of Dust on Fiber Strength," Applied Physics Letters, Vol. 30, (1977), pp. 82-84] or may be physical-chemical alterations in the glass structure, such as structural flaws, bonding defects, such as Si.sup.+ O.sup.- -defects in place of non-polar SiO-bonds. It is also known that fissure propagation generally starts as such localized flaws in glass, particularly in the presence of atmospheric water vapor [see Applied Physics Letters, Vol. 28 (1976) pages 721-723]. Of course, this has an unfavorable effect on the long-term behaviorly strength characteristics of any affected glass fibers.
Various functional or application measures for maximizing the specific strength behavior of glass fibers are known. For example, production and manipulation of raw glass fibers under dust-free conditions is described in Applied Physics Letters Vol. 30 (1977) pages 82-84. A process of coating individual glass fibers with a dense or loose synthetic material is described by H. Schonhorn et al., "Epoxy Acrylate Coated Fused Silica Fibers . . . ", Applied Physics Letters, Vol. 29, (1976) pages 712-714. Similarly, application of specific priming materials for chemical inactivation of silica surfaces, means for avoiding any type of mechanical stress on optical fibers or on optical cables, such as providing shock-absorbing layers, braiding or otherwise combining individual optical fibers with stronger-material fibers and/or providing separate pulling elements for fibers or optical cables are known. However, these various prior art techniques for maximizing the strength of glass fibers and/or cables during the production thereof are relatively expensive and materially add to the cost of the ultmate product.